Our work has suggested that insomniacs may have cognitive disorders by day, manifested by a decrease in semantic memory (the ability to retrieve or use material already well learned) and also suggested that cognitive processes during sleep may also be altered. The current study has pursued this possibility, by testing arousal thresholds to meaningless and meaningful stimuli during sleep, ability to respond to commands during sleep, and similar measures. Among our tentative findings are the observation that insomniacs have decreased ability to differentiate between meaningless and meaningful stimuli during sleep.